A multisite, randomized, controlled clinical effectiveness trial was conducted for osteoarthritis patients with chronic pain of the knee or hip. Adult health nurse practitioners provided a 10-session intervention, pain coping skills training (PCST), in patients’ doctors’ offices (N = 129 patients); the control group received usual care (N = 127 patients). Primary outcomes assessed at baseline, posttreatment, 6-month follow-up, and 12-month follow-up were: pain intensity, physical functioning, psychological distress, self-efficacy, catastrophizing, use of coping strategies, and quality of life. Secondary measures included fatigue, social functioning, health satisfaction, and use of pain medication. Methods favoring external validity, consistent with pragmatic, effectiveness research, were utilized. Primary ITT and secondary per-protocol analyses were conducted. Attrition was within the expected range: 11% at posttreatment and 29% at 12-month follow-up; rates did not differ between groups. Omnibus ITT analyses across all assessment points indicated significant improvement for the PCST group compared with the control group for pain intensity, physical functioning, psychological distress, use of pain coping strategies, and self-efficacy, as well as fatigue, satisfaction with health, and reduced use of pain medication. Treatment effects were robust to covariates (demographics and clinical sites). Trends in the outcomes across the assessments were examined. All outcomes, except for self-efficacy, were maintained through the 12-month follow-up; effects for self-efficacy degraded over time. Per-protocol analyses did not yield greater effect sizes. Comparisons of PCST patients who were more vs less treatment adherent suggested greater effectiveness for patients with high adherence. Results support the effectiveness of nurse practitioner delivery of PCST for chronic osteoarthritis pain.